1. Field of the Invention
The present invention relates to a phosphor comprising an ALN crystal (aluminum nitride crystal) or an ALN solid solution crystal as a host crystal and a manufacturing method thereof and an application thereof. More specifically, the application relates to a lighting device and an emission apparatus of an image display device utilizing features of the phosphor, that is, properties to emit a blue color having a peak spectrum in a wavelength range of 430 nm or longer and 500 nm and shorter. In particular, it relates to an image display device utilizing an excitation electron beam of 10 V or higher.
2. Description of Related Art
The phosphor is utilized in a fluorescent display tube (VFD: vacuum-fluorescent display), a field emission display (FED: Field Emission Display) or SED (Surface-Conduction Electron-Emitter Display), a plasma display panel (PDP: Plasma Display Panel), a cathode-ray tube (CRT: Cathode-Ray Tube), a white light-emitting diode (LED: Light-Emitting Diode), and so on. In any of these applications, it is necessary to provide the phosphor with energy to excite the phosphor in order to have the phosphor emit the fluorescence and the phosphor is excited by an excitation source with high energy such as a vacuum ultraviolet ray, an ultraviolet ray, an electron beam, and a blue light so as to emit a visible light ray. However, the phosphor is exposed to such excitation source that the luminance of the phosphor tends to lower the degree of the brightness. Therefore, the phosphor having little degradation in the brightness is desired. Therefore, a sialon phosphor, an oxynitride phosphor, and a nitride phospher are proposed as a phosphor having little degradation in the brightness instead for the conventional phosphor such as silicate phosphor, phosphate phosphor, aluminate phosphor, and sulfide phosphor.
As an example of these sialon phosphors is manufactured in the following manufacturing process as generally described below. First, silicon nitride (Si3N4), aluminum nitride (AlN), and Europium oxide (Eu2O3) are mixed with predetermined molar ratios and the resultant mixture is fired by a hot press method in one atmospheric pressure (0.1 MPa) of nitrogen atmosphere at 1700° C. for one hour (for example, refer to Patent document 1). It was reported that α-sialon activated with Eu ion manufactured in the above process became a phosphor to emit a yellow light of wavelength range of 550 nm to 600 nm if it is excited by the blue light having a wavelength range of 450 to 500 nm. A phosphor in which a rare-earth element is added to β-type sialon is also known (refer to Patent document 2) and it is shown that phosphors activated by Tb, Yb, and Ag are those which emit a green light of 525 nm to 545 nm. It is also known that β-type sialon activated by Eu2+ becomes a phosphor of green color (refer to Patent document 3).
As an example of the oxynitride phosphor, a blue phosphor activated by Ce having a host crystal of JEM phase (LaAl(Si6-zAlz)N10-zOz) (refer to Patent document 4) and a blue phosphor activated by Ce having a host crystal of La3Si8N11O4 (refer to Patent document 5) are known.
As an example of the nitride phosphor, a red phosphor activated by Eu having a host crystal of CaAlSiN3 (refer to Patent document 6) is known. It is reported in Nonpatent document 1 that an orange or red phosphor having an emission peak from Eu3+ ion in the range of 580 nm to 640 nm was obtained as an amorphous ceramic thin film of phosphor activated by trivalent Eu ion (i.e., AlN: Eu3+) was synthesized by a magnetron sputtering method at the room temperature as a phosphor having AlN as a host. In Nonpatent document 2, it is reported that a phosphor of amorphous AlN thin film activated by Tb3+ emits a green light having a peak at 543 nm upon excitation of an electron beam. In Nonpatent document 3, a phosphor of AlN thin film activated by Gd3+ is reported. However, these kinds of phosphors based on AlN are amorphous thin films which are not suitable for any application of a light or an image display device.
As a blue phosphor for the application of the image display device (VFD, FED, SED, and CRT) having the electron beam as an excitation source, a phosphor having YSiO5 as a host crystal and including solid-solved Ce (Patent document 7) and a phosphor of ZnS including a solid-solved emission ion such as Ag (Patent document 8) are reported.
The present inventor proposed a phosphor having an AlN structure crystal as a host crystal and including divalent Eu ion (i.e., AlN: Eu2+) in Patent document 9 (not yet published). The phosphor can be obtained by firing a composite of AlN to which Si3N4 and Eu2O3 are added at a higher temperature than 1800° C. and shows a blue fluorescence derived from Eu as divalent Eu ions (Eu2+) are stabilized by incorporating Si, Eu, and oxygen into the AlN crystal structure.    [Patent Document 1] Specification of Japanese Patent No. 3,668,770    [Patent Document 2] Japanese Patent Application Publication No. S60-206889    [Patent Document 3] Japanese Patent Application Publication No. 2005-255895    [Patent Document 4] WO 2005/019376    [Patent Document 5] Japanese Patent Application Publication No. 2005-112922    [Patent Document 6] WO 2005/052087    [Patent Document 7] Japanese Patent Application Publication No. 2003-55657    [Patent Document 8] Japanese Patent Application Publication No. 2004-285363    [Patent Document 9] Japanese Patent Application No. 2004-234690    [Nonpatent Document 1] Meghan L. Caldwell, et al., “Visible Luminescent Activation of Amorphous AlN: Eu Thin-Film Phosphors with Oxygen”, MRS Internet Journal Nitride Semiconductor Research, Vol. 6, Num. 13, P 1-8, 2001.    [Nonpatent Document 2] H. H. Richardson, et al., “Thin-film electroluminescent devices grown on plastic substrates using an amorphous AlN: Tb3+ phosphor,” Applied Physics Letters, Vol. 80, No. 12, p. 2207-2209, 2002.    [Nonpatent Document 3] U. Vetter, et al., “Intense ultraviolet cathodoluminescence at 318 nm from Gd3+-doped AlN,” Applied Physics Letters, Vol. 83, No. 11, P 2145-2147, 2003.